An increasing number of consumer products are made from thermoplastic resin such as, for example, adhesive liners and medical gowns. Some consumer products, such as disposable diapers, are primarily made up of thermoplastic resin and cellulosic fiber wherein the thermoplastic material provides a moisture-proof lining on the outside of the diaper and the cellulosic fiber provides the bulky absorbent media on the inside. The cellulosic fiber holds and retains all moisture, while the thermoplastic material ensures that there is no external leakage.
When products such as diapers, adhesive liners, hygiene pads and the like are manufactured, a certain amount of waste is inevitable, resulting in so-called “pre-consumer waste.” In addition, many of these products are disposable in nature and, as a result, are used just once and thrown away resulting in “post-consumer waste.” The ultimate disposal of pre-consumer and post-consumer waste typically involves transporting it to the local landfill. Environmentalists abhor this type of disposal as being wasteful both in the manufacture and disposal of these products. For example, the manufacture of disposable diapers requires forest products to obtain the necessary cellulose and the disposal of the diapers utilizes valuable landfill space. Moreover, the U.S. Environmental Protection Agency (EPA) has placed increase restrictions on landfill requirements. For example, the EPA has recently enforced the requirement of double lining landfills for disposal of paper mill sludge. Consequently, there has been a dramatic increase in cost for establishing new landfills that comply with EPA requirements for paper mill by-products.
In addition to the increased reluctance to use forest products and increased restrictions in landfill requirements, there has also be an increase in demand for new sources of energy. Combustible products made from cellulosic fibers and thermoplastic resins offer a higher BTU output and provide a clean-burning alternative to conventional fuels. However, use of available cellulosic waste as a fuel source has achieved only limited acceptance to date. One reason for this is the relatively low heating value of cellulose as compared to, for example, coal. For example, cellulosic fibers alone can have a heating value of less than 7,000 BTU's per pound, while coal generally has heating value in excess of 9,000 BTU's per pound. Another problem is that many consumer products have substantial tear-resistant properties because the polymers are highly cross-linked or otherwise heavily processed, making these products exceptionally difficult to shred or extrude.
Methods and systems for processing materials consisting substantially of thermoplastic resin and cellulosic fiber into combustible materials are well known in the art. Typically, these processes consist of placing the materials in slow-speed, high-torque shredders where the material is shredded to a consistent size and then moved by a conveyor line to a “cuber,” or extrusion machine, where fuel cubes are extruded under pressure. However, there are a number of problems that arise with this process.
For example, in recent years, many companies have made significant advances in improving the tear-resistant properties of thermoplastic materials. These highly tear-resistant materials, by their very nature, are exceptionally difficult to process using conventional means. If these materials are processed through normal shredder devices, the shredder will quickly become bound-up and, in many cases, cease operating. Moreover, because the materials are combustible by nature, they have a propensity for catching fire if exposed to high heat or friction, such as during processing. As a result, if the operator is successful in maintaining the operation of the shredder, the friction involved in processing these materials creates an extreme fire hazard. There is a need, therefore, for a system for managing the processing of tear-resistant thermoplastics whereby the risk of fire hazard can be minimized.
In addition, because of the wide variety of materials included within the feeder stock, it is very common for the feeder to jam. Such jams are quite costly in terms of the downtime required to clear the jam as well as accumulating excessive wear on the machinery which results in an increase in the costs of both scheduled and non-scheduled maintenance. In addition, because the production level is inconsistent, it is difficult to integrate quantifiable and consistently measurable parameters into a closed loop system. In short, there is a need for a simple, highly intuitive system and method for monitoring and controlling the cuber, in which all key system process parameters can be read at a glance and adjusted in a matter of moments.
Historically, these systems have been managed through the use of traditional “switch and knob” interfaces. However, due to the number of elements involved in even a small cuber installation, such control panels consisted of literally hundreds of lever switches, push buttons, dials and meters that were spread over an area of many tens of square feet. Managing the safe and efficient flow of material through the cuber using this type of system is exceptionally difficult and often results in substantial downtime because the operator is unable to effectively manage all of the variables in the system.
Because of the difficulty in managing such a complex system using switches and knobs, some manufacturers have attempted to automate the process. In those instances, a portion of the switches and knobs described above have been replaced with first-generation touch screen panels. These interfaces provide a very limited, simple, graphical interface whereby systems or subsystems within the process are represented as a box, cylinder or the like. Although it can be appreciated that the graphical interface offers advantages over switches and knobs, the improved interface does not provide an effective means of managing the variables inherent in the operation of the cuber.
To understand the importance of an effective cuber control system, it is instructive to examine the complexities associated with the management of the flow of feedstock into the cuber. Under certain circumstances, the operator may simply fix the feed rate at a rate considerably lower than that which could potentially be supported by the process equipment. In this system, a rate is set on the variable speed drive (VSD) so that the greatest fluctuations in the cuber supply stream coupled with the minimum acceptable density/compressibility factors of the cubes would not exceed the ability of the cuber drive system to supply sufficient torque to the machinery to cube the input stream. This technique results in less jamming of the cuber, but employs the machinery at a rate significantly below its optimal potential so that plant production is artificially limited.
Alternatively, the operator may set the feed rate at a level significantly above that used in the above example. The person then attempts to monitor the cuber load factors using several means, including watching an ammeter displaying cuber motor current, listening to the sounds produced by the feeder and cuber, and “seat-of-the-pants” intuition. This technique results in short periods of high production, but greatly increases plant downtime due to jams resulting from over-feeding as well as outright equipment failure due to the machinery being exposed to significant overload situations occurring at a high frequency relative to overall runtime.
There is a need, therefore, for a compact, inclusive system for managing the operation of a cuber including startup of the equipment, heat monitoring and control during processing, alarm annunciation and acknowledgment, ancillary control shutdown and end-of-production shut down.
There is also a need for a cuber management system that is easy to learn and facilitates training of new operators.